1. Field of the Invention
This invention relates to elastomeric polydiorganosiloxane compositions using extending type fillers.
2. Description of the Prior Art
Elastomeric polydiorganosiloxane compositions are commercially available as fully compounded stocks and as bases which are further compounded by the addition of materials such as catalyst, pigments, and extending fillers. When extending fillers are added, the tensile strength of the cured composition is lowered. Part of the lost strength may be recovered by post-curing the composition.
In U.S. Pat. No. 3,341,489, Simpson discloses that if a certain olefinically unsaturated organosilicon material, such as vinyltriethoxysilane, is employed in minor amounts in an organopolysiloxane composition convertable to the cured, solid, elastic state, the resulting composition can be directly fabricated to valuable elastomeric products without the necessity of an extended post-cure. The olefinically unsaturated organosilicon material is selected from a silane having the formula, ##STR1## and a cyclic siloxane ester having the formula, ##STR2## where R' is an olefinically unsaturated monovalent hydrocarbon radical, R" is a member selected from hydrogen, and monovalent hydrocarbon radicals free of olefinic unsaturation, R''' is a divalent aliphatic radical, X is a member selected from alkoxy radicals, alkoxyalkoxy radicals, alkoxyaryloxy radicals, acyloxy radicals, and halogen radicals, Y is a member selected from R" and X radicals, b is a whole number equal to from 0 to 2 inclusive, c is an integer equal to from 1 to 3 inclusive, and the sum of b and c is equal to 3, and n is an integer equal to from 1 to 10, and preferably from 1 to 3 inclusive. The invention is practiced by forming a mixture of the polymer, filler, and organosilanes; the order of addition is not critical.
There is no teaching in the above patent that an acryloxyalkylsilane will increase the tensile strength of a compound made with an extending filler such as ground silica and a silicone rubber base.
In U.S. Pat. No. 3,567,497, Plueddemann and Clark teach the use of an acryloxyalkylsilane with a polymerizable vinylic resin and a base member to produce a composite article of superior strength. They teach that all siliceous materials including clay, diatomaceous earth, and ground quartz are useful in their invention. The vinylic resins described as of greatest interest are styrene, acrylic, methacrylic, and polyester resins; and butadiene-styrene copolymers.
The preferred method of use is to wet the surface of the base member with an aqueous solution of a hydrolysate of the defined silane, then allowing the surface to dry to yield a treated base member.
They teach that the treated materials of their invention can also be incorporated into natural polyolefinic rubber articles. Other types of rubbery materials which can be employed are organosiloxane rubbers which contain at least some silicon atoms to which are attached unsaturated aliphatic radicals.
Although the acryloxyalkylsilane of the instant invention is taught by Plueddmann and Clark, they do not teach the instant invention. They teach the addition of an acryloxyalkylsilane to a vinylic resin and thereafter applying the mixture to a base member or filler.
It is known that silanes containing vinyl and methacryl functionality may be used with mineral-filled peroxide-cured elastomers including EPR, EPDM, silicone elastomers, and crosslinkable polyethylene. It is broadly taught that the use of silanes at concentrations ranging from less than 0.5 parts by weight per hundred filler to levels above 2.0 parts by weight per hundred filler improve the performance of relatively inexpensive extending fillers, including ground silica, calcined and hydrous clay, talc, wollastonite, alumina trihydrate, calcium carbonate, and titanium dioxide.